CI: Appveyor broke with unknown 'l' in printf format

For unknown reasons, all the sudden all our PRIuXX macro usage exploded with this warning (as an example but everything explodes):

../src/app/main/main.c:414:9: error: unknown conversion type character 'l' in format [-Werror=format=]
  414 |         "Average bandwidth: %"PRIu64"/%d = %d bytes/sec reading",
      |         ^~~~~~~~~~~~~~~~~~~~~~

https://ci.appveyor.com/project/torproject/tor/builds/33955351/job/tsqab8smrp645sk2?fullLog=true